ADS7846 regulator is disabled twice in a row in ads7846_remove(). Valid
one is in ads7846_disable().

Removing the ads7846 module causes warning about unbalanced disables.

  ...
  WARNING: CPU: 0 PID: 29269 at drivers/regulator/core.c:2251 _regulator_disable+0xf8/0x130
  unbalanced disables for vads7846
  CPU: 0 PID: 29269 Comm: rmmod Tainted: G      D W       4.7.0+ #3
  Hardware name: HTC Magician
  ...
    show_stack+0x10/0x14
    __warn+0xd8/0x100
    warn_slowpath_fmt+0x38/0x48
    _regulator_disable+0xf8/0x130
    regulator_disable+0x34/0x60
    ads7846_remove+0x58/0xd4 [ads7846]
    spi_drv_remove+0x1c/0x34
    __device_release_driver+0x84/0x114
    driver_detach+0x8c/0x90
    bus_remove_driver+0x5c/0xc8
    SyS_delete_module+0x1a0/0x238
    ret_fast_syscall+0x0/0x38

Signed-off-by: Petr Cvek <petr.cvek@tul.cz>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>